I don't think there is anything you can do now given you have already told them your salary, and ideally you had to at some point.
So rather, i would suggest just do some thorough research here and on fishbowl with peers in same company and designation about what range to expect. That way you know what is the ideal range, and if they come back with lowballed offer, you can make a point that it seems too low as per what you know of company standards without taking any names.
In Investment banking, i dont think it can ever work if i don't reveal my salary in the first call from HR to understand the match for profile, and no matter how much you ask, they won't tell you their range.
So the only option is what i said above, research and find from peers.